European Parliament Election on Sunday Will Serve as a Test of Strength for Secessionist Parties

MADRID—Sunday's European Parliament election will serve as a test of strength for secessionist parties in Catalonia, amid a rancorous debate over the wealthy region's proposed referendum on independence from Spain.

The voting in Catalonia, which features a highly polarized electorate and faltering establishment political parties, will be watched in Spain as closely as the battle between conservatives and socialists at a national level. Catalonia generates about one-quarter of Spain's exports and the maneuvering around the...